The proposal is for support of a Program Project on the Comparative Neurobiology of the Spinal Cord. The team of investigators is engaged in a multidisciplinary, highly interactive research program using a variety of vertebrate animal models. The projects can be grouped under three major subheadings. The first set of projects (A Method for Assessing Neural Sprouting in the Dorsal Horn; Nerve Growth Factor: Axonal and Synaptic Changes in the Spinal Cord; and Primary Afferent and Propriospinal Fibers in the Spinal Cord) are directed at the analysis of the synaptic input to the dorsal horn of the spinal cord and plastic changes that occur in that input as a result of injury. The second group of projects (A Light and EM Analysis of Chemically Identified Terminals on Primate STT Neurons; Catecholamine Projections to Primate STT Cells and Thalamus; Development of Identified Ventrolateral Funiculus Ascending Tract Cells; Neurotransmitter Release in Conjunction with Analgesia in the Spinal Cord; and Nociceptive Sensory Transmission and Reaction) are concerned with an analysis of the morphological and physiological basis of the spinal cord circuitry underlying nociception and the neural systems that can be used to control pain. The third cluster of projects (Integrative Mechanisms in Lamprey Spinal Cord; Propriospinal Neurons in Locomotion; and Uptake of Antibodies by Spinal Cord Motor Neurons) are oriented toward interneuronal activity and the motor output of the spinal cord. The first assumption of the work proposed is that a more detailed understanding of the circuitry of the spinal cord will be required before it will be possible to determine ways for improving recovery from spinal cord injury, for alleviating pain more effectively and for enhancing motor activity in individuals suffering from motor deficits. The comparative approach may facilitate the required analysis, since the choice of the best animal model can be made from a spectrum of vertebrate forms. The second assumption is that the emphasis of our analysis should be on synaptic connectivity in defined neural systems. The use of immunocytochemistry and neurochemical analysis will supplement more traditional morphological and electrophysiological approaches. The spinal cord systems that will be studied most intensively include the primary afferent input to the dorsal horn, the pain transmission system and the locomotor system.